Tinnitus is a phantom sound percept that exists without any external sound source. Although it is known as ringing in the ear, it is actually a neurological disorder in which abnormal signaling patterns occur in brain regions responsible for auditory perception. Tinnitus continues to be underestimated in terms of its negative impact in society because it is not a condition that is visible to the public. About 250 million people worldwide experience chronic tinnitus that can be bothersome on a daily basis. In the U.S. alone, approximately 16 million people have sought medical attention for tinnitus, with 2-3 million experiencing debilitating and even suicidal conditions (e.g., related to annoyance, depression, anxiety, headaches, insomnia). Considering the link between tinnitus and hearing loss, these numbers will continue to rise due to increased noise in our environment, a larger elderly population, and greater noise-based war injuries. In fact, tinnitus is currently the highest service-connected disability for veterans and the top war-related health cost. Unfortunately, there is no cure or reliable treatment for tinnitus. Various drug therapies, neural and mechanical stimulation methods, psychotherapy, and sound treatments have been attempted but with mixed results.
There is a general consensus in the tinnitus field that most of the tinnitus cases are linked to some form of hearing loss that alters the firing patterns in the auditory system and leads to tinnitus, and thus approaches for restoring hearing loss including hearing aids and cochlear implants can serve as potential solutions. It is not possible to provide a cochlear implant to most of these patients because this device can compromise their residual hearing since the implant is inserted into the cochlea. Hearing aids can amplify sounds to attempt to restore hearing but in most tinnitus patients, this hearing restoration is insufficient to treat the tinnitus. Due to these limitations, a majority of researchers attempt to find ways to modulate the brain with devices, drugs, or psychotherapy/counseling to shift the abnormal brain patterns back to normal or at least to a stable state without the tinnitus percept. Currently, there is no consistent or reliable method for treating tinnitus. Some approaches work in some tinnitus patients, but there is no way yet to predict beforehand who will respond to a given treatment. As a result, clinicians or audiologists can only provide a list of “potential” solutions to the patients, which typically includes counseling to deal with the tinnitus or a tinnitus masker. Tinnitus maskers are devices that present different types of sounds to attempt to interfere with or suppress the tinnitus percept though they typically do not sufficiently alter the brain activity to be effective in most patients. If the tinnitus is more bothersome to the patient, he or she can be prescribed anti-depressants or anti-anxiety medications to help cope with the tinnitus but these do not necessarily treat the tinnitus percept.
Since research in the tinnitus field has demonstrated abnormal brain patterns in tinnitus patients and animals, it has become increasingly accepted by scientists and clinicians that one way to treat tinnitus is to shift the abnormal neural activity to a near-normal or non-tinnitus state. There are various investigational approaches to alter this abnormal tinnitus activity, known as neuromodulation devices. Electrodes can be implanted into the brain or nerves for direct electrical stimulation. Noninvasive approaches using magnetic (TMS) and electrical (tDCS, tACS, TENS) fields or even mechanical inputs (e.g., acupuncture, body movements/exercise) can also be attempted. Invasive approaches require risky surgery and are expensive, limiting the number of patients who can benefit from those treatments. The noninvasive approaches have not shown sufficient brain changes to treat tinnitus consistently across patients. Accordingly, more improved methods to treat tinnitus are needed.
In terms of hearing loss, more than 5% of the population (more than 360 million people) have disabling hearing loss (according to the World Health Organization). The most common solution is to wear a hearing aid. Hearing aids are designed to amplify sound features that the patient cannot hear sufficiently. In some cases, this approach works well but in many patients, especially in noisy and complex environments, this approach is insufficient. Simply amplifying these different sound features, especially different frequency components (i.e., many have hearing deficits for specific or a range of sound frequencies), causes them to distort or mask other sound features. Furthermore, amplifying sounds causes feedback issues for hearing aids since the sound that is amplified can be picked up again by the microphone, which in turn gets re-amplified and so on.
What would be a major breakthrough in the hearing aid field is if we could increase the gain of those desired sound features in the brain (and suppress the unwanted sound features) rather than physically at the output of the hearing aid to the ear. There are damaged portions of the middle and inner ear that lead to deficits in hearing of specific sound features. Unless those damaged portions are fixed, then the only way to overcome those deficits is to amplify those sound features to get them through those damaged portions. Amplifying those sound features can create significant distortion of the original sound input and even become uncomfortable or unintelligible for the patient. Accordingly, more improved methods to treat hearing loss are needed.